KR20030029165A - Fuel cell and production method therefor - Google Patents

Abstract

In the present invention, a fuel electrode and an oxygen electrode are provided, and the fuel electrode and the oxygen electrode are disposed to face each other via a proton conductor film. The fuel electrode and the oxygen electrode have carbonaceous material powder as an electrode material, and on the surface thereof, a proton conductor having a basic composition of proton dissociation in a carbonaceous material mainly composed of carbon exists. In producing such an electrode, a carbonaceous material powder serving as an electrode material may be immersed in a solvent containing a proton conductor in which proton dissociation is introduced into a carbonaceous material composed mainly of carbon. A carbonaceous material containing carbon as a main component, for example, a proton conductor in which proton dissociation is introduced into a carbon cluster or carbon nanotube such as fullerene, exhibits good proton conductivity without being humidified.

Description

Fuel cell and production method therefor {Fuel cell and production method therefor}

Recently, alternative clean energy sources are desired to replace fossil fuels such as oil. Hydrogen gas fuel is drawing attention as an energy source of this kind.

Hydrogen can be said to be an ideal energy source that is clean and inexhaustible because of the large amount of chemical energy contained per unit mass and the fact that it does not emit harmful substances, global warming gases, etc. in use.

Background Art In recent years, development of fuel cells that can extract electric energy from hydrogen energy is in full swing. On-site self-power generation in large-scale power generation, and furthermore, application as a power source for electric vehicles is expected.

In a fuel cell, a proton conductor membrane is sandwiched with a fuel electrode, for example, a hydrogen electrode and an oxygen electrode, and hydrogen and oxygen as fuel are supplied to these electrodes to cause a cell reaction to obtain an electromotive force. Usually, a proton conductor film, a fuel electrode, and an oxygen electrode are shape | molded, respectively, and these are bonded together.

In this type of fuel cell, how to smoothly carry out proton conduction becomes important in order to improve battery characteristics.

For example, it is considered effective to coat the electrode material with a proton conductor and to smoothly move the proton from the electrode to the proton conductor film via the proton conductor.

Materials that have been examined as proton conductors so far, for example, polymer materials of proton (hydrogen ion) conductivity such as perfluorosulfonic acid resins, need to be humidified in order to maintain good proton conductivity, and are good in a dry atmosphere. There is a problem that proton conductivity is not maintained.

In addition, the polymer material as described above has a problem in terms of electron conductivity. In the fuel electrode, not only the proton conduction but also the electrons need to move quickly to the terminal. When a polymer material is used, the electron conductivity tends to be poor and the internal resistance tends to increase.

The present invention relates to a fuel cell which obtains electromotive force by the reaction of a fuel, for example hydrogen and oxygen, and a method of manufacturing the same.

The present invention has been proposed in view of the above circumstances, and an object of the present invention is to provide a fuel cell and a method of manufacturing the same, which can maintain a good proton conductivity even in a dry atmosphere and do not reduce output.

In order to achieve the above object, the fuel cell according to the present invention includes a fuel electrode and an oxygen electrode, and these fuel electrodes and the oxygen electrode are disposed to face each other via a proton conductor film. In both of the fuel electrode and the oxygen electrode, a proton conductor in which carbonaceous powder is used as an electrode material and proton dissociation is introduced into a carbonaceous material mainly composed of carbon on its surface.

In the production method of the present invention, a carbonaceous material powder serving as an electrode material of a fuel electrode and / or an oxygen electrode is added to a solvent containing a proton conductor in which proton dissociation is introduced into a carbonaceous material containing carbon as a main component. The surface is covered with a proton conductor.

As used herein, the term "proton dissociative property" means a functional group capable of dropping protons (H +) by ionization.

A carbonaceous material containing carbon as a main component, for example, a proton conductor in which proton dissociation is introduced into a carbon cluster such as fullerene, carbon nanotube, or the like, exhibits good proton conductivity without humidification.

If a proton conductor exists on the surface of the carbonaceous material powder as an electrode material, sufficient proton conductivity is maintained even in a dry atmosphere.

Since the electrode material coated with the proton conductor is a carbonaceous material, it also has good electron conductivity.

Further objects of the present invention and the specific advantages obtained by the present invention will become more apparent from the description of the embodiments described below.

Detailed Description of the Drawings

1 is a schematic cross-sectional view showing the basic configuration of a fuel cell.

Fig. 2 is a schematic diagram showing the coating state of the carbonaceous material powder by the proton conductor.

3 is a schematic diagram showing various examples of a carbon cluster.

It is a schematic diagram which shows the partial fullerene structure which is another example of a carbon cluster.

5 is a schematic diagram showing a diamond structure as another example of a carbon cluster.

It is a schematic diagram which shows that cluster which is another example of a carbon cluster couple | bonds.

7 is a schematic diagram showing an example of an arc discharge device for producing carbon nanotubes.

8A, 8B, and 8C are schematic diagrams showing various carbonaceous materials contained in the carbon iron sheet produced by arc discharge.

9 is a schematic diagram illustrating a specific configuration example of a fuel cell.

10 is a characteristic diagram showing the output characteristics of the fuel cell according to the present invention in comparison with that of the comparative example.

EMBODIMENT OF THE INVENTION Hereinafter, the fuel cell to which this invention is applied, and its manufacturing method are demonstrated in detail, referring drawings.

The fuel cell according to the present invention has the configuration as shown in FIG. 1, and as a basic configuration, the fuel electrode 2 and the oxygen electrode 3 are respectively provided on both surfaces of the proton conductor film 1 having proton conductivity. To form.

In this fuel cell, when hydrogen is supplied to the fuel electrode 2, for example, and oxygen is supplied to the oxygen electrode 3, a battery reaction occurs to generate electromotive force. Here, in the so-called direct methanol system, methanol can be supplied to the fuel electrode 2 as a hydrogen source.

The fuel electrode 2 and the oxygen electrode 3 are formed by forming a carbonaceous material powder as an electrode material and molding the same. In the present invention, as shown in FIG. 2, the surface of the carbonaceous material powder 4 is formed. Is coated with the proton conductor 5, and the conduction of the proton proceeds smoothly. 2, the catalyst metal 6 used as a reaction point of hydrogen is also shown.

For example, when the fuel electrode 2 adopts the above form, when the fuel supplied is hydrogen, the catalyst metal 6 is first converted into protons and electrons as reaction points. Of these, protons move to the proton conductor film 1 via the proton conductor 5. On the other hand, the electrons quickly flow to the terminal due to the electron conductivity of the carbonaceous material powder 4 which is the base material of the electrode 2.

In addition, in order to coat the surface of the carbonaceous material powder 4 with the proton conductor 5, the proton conductor may be dispersed in a solvent, and the carbonaceous material powder may be dipped and then dried.

As the proton conductive material constituting the proton conductor 5, a proton conductor formed by using a carbonaceous material composed mainly of carbon as a mother matrix and introducing the base of proton dissociation therein is most suitable.

Here, as the primary sex proton dissociation, and the like _{-OH, -OSO 3 H, -SO 3} H, -COOH, -OP (OH) 2.

In this proton conductor, protons move through the base of proton dissociation and ionic conductivity is expressed.

As the base carbonaceous material, any material can be used as long as carbon is a main component. However, it is necessary that the ion conductivity is larger than the electron conductivity after introducing the base of proton dissociation.

Specifically, the carbon cluster which is an aggregate of carbon atoms, the carbonaceous material containing tubular carbonaceous, ie, carbon nanotube, etc. are mentioned.

There are various kinds of carbon clusters, and most suitable are those having an open end at least in part of a fullerene or fullerene structure or having a diamond structure.

Hereinafter, this carbon cluster will be described in more detail.

A cluster is usually an aggregate formed by bonding or agglomeration of several hundreds of atoms, and when the atoms are carbon, the aggregate improves proton conductivity and maintains chemical properties to provide a sufficient film strength. Easy to form. The term "carbon-based cluster" refers to an aggregate in which carbon atoms are formed by several to hundreds of bonds regardless of the kind of carbon-carbon bonds. However, it is not necessarily composed of only 100% carbon, and there may be a mixture of other atoms. Including such a case, the aggregate in which a carbon atom occupies a lot is called a carbon cluster. When this aggregate is demonstrated by drawing, it is as showing in FIG. 3 thru | or 6, and the selection of a proton conductor as a raw material is wide. In addition, the base of proton dissociation is abbreviate | omitted here.

3 shows various carbon clusters having a spherical or long sphere made of a plurality of carbon atoms, or a closed surface structure similar to these. However, it also shows as a molecular fullerene. In contrast, various carbon clusters in which some of their spherical structures are missing are shown in FIG. 4. In this case, the structure is characterized by having an open end in the structure, and such a structure can be seen as a large number of by-products in the process of producing fullerene by arc discharge. When most of the carbon atoms of the carbon clusters are bonded to SP3, various clusters having a diamond structure as shown in Fig. 5 form.

Fig. 6 shows various cases in which clusters are bonded to each other, and even such a structure can be applied to the present invention.

Proton conductors containing a carbonaceous material having a base of proton dissociation as a main component are protons easily dissociated from the group even in a dry state, and furthermore, the protons have a wide temperature range including room temperature, at least about 160 ° C to -40 ° C. It is possible to exhibit high conductivity over the range of. As described above, the proton conductor exhibits sufficient proton conductivity even in a dry state, but may be present in water. This moisture may have invaded from the outside.

On the other hand, any carbonaceous material may be used for the carbonaceous material powder 4 used as the electrode material, but in particular, such as carbon nanotubes or needle-like graphite (for example, manufactured by Toho Rayon Co., Ltd., trade name VGCF). It is preferable that a needle-like carbonaceous material is included.

7 shows an example of an arc discharge device for producing a carbonaceous material including carbon nanotubes. In this apparatus, in the reaction chamber 11 called a vacuum chamber, both the cathode 12 and the anode 13 made of carbon rods such as graphite are disposed to face each other via the gap G, and the rear end of the anode 13 It is connected to the linear motion introduction mechanism 14, and each pole is connected to the current introduction terminals 15a and 15b, respectively.

In such a configuration, after degassing the inside of the reaction chamber 11, the gas is filled with a rare gas such as helium, and a direct current is supplied to each electrode, so that an arc discharge occurs between the cathode 12 and the anode 13. On the inner surface of the reaction chamber 11, that is, the side wall surface, the ceiling surface, the bottom surface and the cathode 12, iron-like carbonaceous material is deposited. In addition, when a small container is previously attached to the side wall surface or the like, a carbonaceous material is deposited therein.

The iron type carbonaceous material recovered from the reaction chamber 11 contains a carbon nanotube as shown in FIG. 8A, a C60 fullerene as shown in FIG. 8B, and a C70 fullerene not shown but a carbon iron as shown in FIG. 8C. It is. This carbon iron sheet is an iron sheet having a curvature not grown by fullerene molecules or carbon nanotubes. In addition, typical compositions of the iron type carbonaceous material include 10 to 20% of fullerenes such as C60 and C70, several% of carbon nanotubes, and a large amount of carbon iron.

In the carbonaceous material, at least 20 wt% or less of a metal having a catalytic ability capable of separating hydrogen molecules into hydrogen atoms, and further from protons and electrons, is supported on at least the surface thereof by a known method. Do. As a metal which has a catalytic capability, platinum, a platinum alloy, etc. are mentioned, for example. Supporting such a catalyst metal can increase the efficiency of the battery reaction as compared with the case where the catalyst metal is not supported.

In the case of using the needle-like carbonaceous material described above, the fuel electrode 2 or the oxygen electrode 3 can be formed directly on the proton conductor film 1. As the forming method, a spray method or a dropping method may be mentioned.

In the case of the spraying method, the carbonaceous material is dispersed in a solvent such as water or ethanol and sprayed directly onto the proton conductor film 1. In the case of the dropping method, the carbonaceous material is further dispersed in a solvent such as water or ethanol, and this is directly added to the proton conductor film 1.

As a result, the carbonaceous material is laid down on the proton conductor film 1. In this case, the carbon nanotubes have a shape of a thin and long fiber having a diameter of about 1 to 3 nm and a length of about 1 to 10 μm, and the needle-like graphite has a needle shape of about 0.1 to 0.5 μm in diameter and about 1 to 50 μm in length. For the sake of illustration, it is entangled with each other and constitutes a good layered body even without a special binder. Of course, it goes without saying that it is also possible to use a binder (binder) together as needed.

Since the fuel electrode 2 or the oxygen electrode 3 formed by the above-described method does not need to be self-supporting, mechanical strength is not required. Therefore, the thickness thereof is 10 μm or less, for example, about 2 to 4 μm. Wow, it can be set very thin.

In the fuel cell configured as described above, any material can be used for the proton conductor film 1 as long as it has a proton conductivity. For example, the thing which apply | coated and supported the material which has proton conductivity to a separator, etc. can also be used.

Specifically, as a material which can be used for the proton conductor film 1, first, a proton (hydrogen ion) conductive polymer material such as a perfluorosulfonic acid resin (for example, manufactured by DuPont, trade name Nafion (R)) is used. Can be mentioned.

As other proton conductors, polymolybdates and oxides having a large number of hydrated water, such as H ₃ Mo ₁₂ PO ₄₀ · 29H ₂ O and Sb ₂ O ₅ · 5.4H ₂ O, which have been recently proposed, can also be used.

These polymer materials and hydrated compounds exhibit high proton conductivity near room temperature when placed in a wet state.

In other words, taking a perfluorosulfonic acid resin as an example, the protons isolated from the sulfonic acid group are water protonated by combining (hydrogen bond) with water collected in large quantities in the polymer matrix, that is, oxonium ion (H ₃ O ^1). ), Take the form of this oxonium ion, and the proton can move smoothly in the polymer matrix, this kind of matrix material can exhibit a significantly high proton conduction effect even at room temperature.

Alternatively, a proton conductor may be used which is entirely different from the material thereof.

In other words, such a complex metal oxide having the perovskite structure such as SrCeO ₃ doped with Yb. It has been found that composite metal oxides having this kind of perovskite structure have proton conductivity even when water is not used as a transfer medium. In this composite metal oxide, it is considered that protons are conducted by in-vehicle alone between the oxygen ions forming the skeleton of the perovskite structure.

However, also in this proton conductor film 1, since the necessity of humidification etc. becomes a problem, the same material as the said proton conductor 5, ie, the carbonaceous material which has carbon as a main component as a base material, It is preferable to use a proton conductor formed by introducing a proton dissociable group.

Fig. 9 shows a specific structural example of the fuel cell in which the above-described electrode and proton conductor are incorporated.

The fuel cell has a negative electrode (fuel electrode or hydrogen electrode) 28 and a positive electrode (oxygen electrode) 29 facing each other in which the catalysts 27a and 27b are brought into close contact with or dispersed therein, and a proton conductor portion between these anodes. 30 is sandwiched. Terminals 28a and 29a are drawn out from the negative electrode 28 and the positive electrode 29, respectively, and have a structure for connecting with an external circuit.

In this fuel cell, in use, hydrogen is supplied from the inlet port 31 on the negative electrode 28 side and discharged from the outlet port 32. In addition, the discharge port 32 may not be provided. Protons are generated while the fuel (H ₂ ) 33 passes through the flow path 34, which moves along with the protons generated in the proton conductor portion 30 to the positive electrode 29 side, where at the inlet 31 It reacts with oxygen 38 or air supplied to the flow path 36 toward the exhaust port 37, whereby the desired electromotive force is extracted.

In the above configuration, the hydrogen supply source 39 houses a hydrogen storage alloy and a carbonaceous material for hydrogen storage. In addition, hydrogen may be stored in this material in advance, and may be stored in the hydrogen supply source 39.

Example 1

Here, a fuel cell according to the present invention was produced, and its output characteristics were measured. As shown in Fig. 2 described above, this fuel cell is attached with a sulfonated fullerene (C ₆₀ or C ₇₀ ) to the fuel electrode 2 mainly composed of a carbon material. In order to melt | dissolve in alcohol or THF, this adhesion | attachment material was dripped so that 1 M solution might be 1 wt% with respect to electrode weight. The dropping was carried out with a dropper. The solvent was sufficiently dried in a dry atmosphere and the output characteristics were measured. This output characteristic was performed under the condition that the dry hydrogen gas was passed through the fuel cell and the dry air was passed through the oxygen electrode.

The output observed a change over time. The result is as showing to FIG. 10A.

Comparative Example 1

Comparative Example 1 was produced in comparison with the fuel cell according to the present invention. In Comparative Example 1, a polymer solid electrolyte solution (Nafion) was added to the fuel electrode in the same weight ratio. The output characteristics of the battery were measured. This output characteristic was carried out under the conditions in which dry hydrogen gas was passed through the fuel cell and dry air was passed through the oxygen electrode in the same manner as in Example 1.

The output observed a change over time. The result is as showing to FIG. 10B.

The present invention can maintain a good proton conductivity even in a dry atmosphere, and can realize a fuel cell in which the output does not decrease.

Claims (8)

In a fuel cell comprising a fuel electrode and an oxygen electrode, the fuel electrode and the oxygen electrode are arranged to face each other via a proton conductor film, In the fuel electrode and / or the oxygen electrode, a fuel cell characterized in that a proton conductor having a carbonaceous material powder as an electrode material and having proton dissociation thereon in a carbonaceous material containing carbon as its main component is present on the surface thereof. . The method of claim 1, The carbonaceous material powder comprises a needle-like carbonaceous material. The method of claim 2, And the needle-shaped carbonaceous material is carbon nanotube or needle-shaped graphite. The method of claim 1, And the fuel electrode and / or the oxygen electrode carry a catalyst metal. The method of claim 4, wherein The catalyst metal is a fuel cell, characterized in that the platinum or alloys thereof. The method of claim 1, And a proton conductor constituting the proton conductor membrane and a proton conductor present on the surface of the carbonaceous material powder. The method of claim 1, A carbonaceous material which is a base material of the proton conductor includes a carbon cluster or carbon nanotubes. A carbonaceous material powder serving as an electrode material of a fuel electrode and / or an oxygen electrode is added to a solvent containing a proton conductor in which proton dissociation is introduced into a carbonaceous material containing carbon as a main component, and the surface of the proton conductor Method of manufacturing a fuel cell, characterized in that the coating.